---
title: JTAG
---
<h1>JTAG Application</h1>

<p>This application serves for the debugging of generic JTAG devices of all types,
and the macros that it defines serve as the basis for other JTAG debugging applications,
such as the one for the MSP430.</p>

<p>The pinout is standard for the MSP430 FET.</p>

<h2>Clients</h2>

<p>Please write one.</p>

<h2>Development</h2>

<p>Prior to any transaction, the SETUP (0x10) verb should be sent to the JTAG application
to properly set the I/O pin directions.  After that, the START (0x20) and STOP (0x21)
verbs may be used to enter and exit the TAP.</p>

<p>The JTAG protocol itself is rather barren, defining only the setting and clearing
of the Instruction Register (IR) and Data Register (DR).</p>

<h2>Verbs</h2>

<p>The following verbs are supported.</p>

<table border="1">
<tr><th>Hex</th><th>#define</th><th>Description</th></tr>
<tr><td>0x10</td><td>SETUP</td><td>Configure I/O pins.</td></tr>
<tr><td>0x20</td><td>START</td><td>Start a transaction.</td></tr>
<tr><td>0x21</td><td>STOP</td><td>Stop a transaction.</td></tr>
<tr><td>0x7E</td><td>NOK</td><td>No Operation</td></tr>

<tr><td>0x80</td><td>IR_SHIFT</td><td>Shift the IR.</td></tr>
<tr><td>0x81</td><td>DR_SHIFT</td><td>Shift the DR.</td></tr>
<tr><td>0x91</td><td>DR_SHIFT20</td><td>Shift 20 bits of DR.</td></tr>
</table>
